/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.handler.codec.http.websocketx.extensions;

import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPromise;
import io.netty.handler.codec.CodecException;
import io.netty.handler.codec.http.HttpHeaderNames;
import io.netty.handler.codec.http.HttpRequest;
import io.netty.handler.codec.http.HttpResponse;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

/**
 * This handler negotiates and initializes the WebSocket Extensions.
 *
 * This implementation negotiates the extension with the server in a defined
 * order, ensures that the successfully negotiated extensions are consistent
 * between them, and initializes the channel pipeline with the extension decoder
 * and encoder.
 *
 * Find a basic implementation for compression extensions at
 * <tt>io.netty.handler.codec.http.websocketx.extensions.compression.WebSocketClientCompressionHandler</tt>.
 */
public class WebSocketClientExtensionHandler extends ChannelDuplexHandler
{

    private final List<WebSocketClientExtensionHandshaker> extensionHandshakers;

    /**
     * Constructor
     *
     * @param extensionHandshakers The extension handshaker in priority order. A
     *        handshaker could be repeated many times with fallback
     *        configuration.
     */
    public WebSocketClientExtensionHandler(
            WebSocketClientExtensionHandshaker... extensionHandshakers)
    {
        if (extensionHandshakers == null)
        {
            throw new NullPointerException("extensionHandshakers");
        }
        if (extensionHandshakers.length == 0)
        {
            throw new IllegalArgumentException(
                    "extensionHandshakers must contains at least one handshaker");
        }
        this.extensionHandshakers = Arrays.asList(extensionHandshakers);
    }

    @Override
    public void write(final ChannelHandlerContext ctx, Object msg,
            ChannelPromise promise) throws Exception
    {
        if (msg instanceof HttpRequest && WebSocketExtensionUtil
                .isWebsocketUpgrade(((HttpRequest) msg).headers()))
        {
            HttpRequest request = (HttpRequest) msg;
            String headerValue = request.headers()
                    .getAsString(HttpHeaderNames.SEC_WEBSOCKET_EXTENSIONS);

            for (WebSocketClientExtensionHandshaker extentionHandshaker : extensionHandshakers)
            {
                WebSocketExtensionData extensionData = extentionHandshaker
                        .newRequestData();
                headerValue = WebSocketExtensionUtil.appendExtension(
                        headerValue, extensionData.name(),
                        extensionData.parameters());
            }

            request.headers().set(HttpHeaderNames.SEC_WEBSOCKET_EXTENSIONS,
                    headerValue);
        }

        super.write(ctx, msg, promise);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg)
            throws Exception
    {
        if (msg instanceof HttpResponse)
        {
            HttpResponse response = (HttpResponse) msg;

            if (WebSocketExtensionUtil.isWebsocketUpgrade(response.headers()))
            {
                String extensionsHeader = response.headers()
                        .getAsString(HttpHeaderNames.SEC_WEBSOCKET_EXTENSIONS);

                if (extensionsHeader != null)
                {
                    List<WebSocketExtensionData> extensions = WebSocketExtensionUtil
                            .extractExtensions(extensionsHeader);
                    List<WebSocketClientExtension> validExtensions = new ArrayList<WebSocketClientExtension>(
                            extensions.size());
                    int rsv = 0;

                    for (WebSocketExtensionData extensionData : extensions)
                    {
                        Iterator<WebSocketClientExtensionHandshaker> extensionHandshakersIterator = extensionHandshakers
                                .iterator();
                        WebSocketClientExtension validExtension = null;

                        while (validExtension == null
                                && extensionHandshakersIterator.hasNext())
                        {
                            WebSocketClientExtensionHandshaker extensionHandshaker = extensionHandshakersIterator
                                    .next();
                            validExtension = extensionHandshaker
                                    .handshakeExtension(extensionData);
                        }

                        if (validExtension != null
                                && ((validExtension.rsv() & rsv) == 0))
                        {
                            rsv = rsv | validExtension.rsv();
                            validExtensions.add(validExtension);
                        }
                        else
                        {
                            throw new CodecException(
                                    "invalid WebSocket Extension handhshake for \""
                                            + extensionsHeader + "\"");
                        }
                    }

                    for (WebSocketClientExtension validExtension : validExtensions)
                    {
                        WebSocketExtensionDecoder decoder = validExtension
                                .newExtensionDecoder();
                        WebSocketExtensionEncoder encoder = validExtension
                                .newExtensionEncoder();
                        ctx.pipeline().addAfter(ctx.name(),
                                decoder.getClass().getName(), decoder);
                        ctx.pipeline().addAfter(ctx.name(),
                                encoder.getClass().getName(), encoder);
                    }
                }

                ctx.pipeline().remove(ctx.name());
            }
        }

        super.channelRead(ctx, msg);
    }
}
